I have a shlumberger R5 connected with a cable (cut up modem cable RJ11 to 3.5 jack) to the pulse port of emontx v2. It uses the internal Arduino pull up resistor.
I read around on the forums and arrived at developing
A timer and not interrupt based solution. Very, very, stable pulse detection for coming up to a year. Might be an approach to rework for your kit.